From the past, silicone and acrylic-based synthetic resins in powder form are used in a variety of cosmetics such as hair care products, makeup cosmetics, and sunscreens since they form a uniform coating on the surface of skin or hair to keep the skin or hair moisturized and smooth or impart water repellency and water resistance.
For example, JP-A H07-196815 discloses silicone fine particles and JP-A 2001-151626 discloses acrylic resin fine particles. Since they are allegedly non-agglomerative and well dispersible and impart soft tactility, they are suitably formulated in cosmetics. Yet there exists a need for a powdered resin of better performance.
As is known in the art, an attempt is made to copolymerize a silicone component capable of imparting slipperiness and water repellency with an acrylic component capable of imparting compatibility, skin adhesion, and soft tactility. The resulting resin powder is useful in cosmetic application. For example, JP-A H03-162442 and JP-A H04-342513 disclose cosmetic compositions comprising a powdered resin obtained by graft polymerizing silicone to an acrylic backbone. There is still left room for improvement in slipperiness and tactility.
While resins obtained by graft polymerizing an acrylic component to a silicone backbone are also known, few find use in cosmetics. In the cosmetic application, silicone-acrylic copolymer resins based on silicone backbone are expected to be superior in slipperiness and tactility to those resins based on acrylic backbone. JP-A H05-078681 discloses a powdered resin based on a silicone component and having an acrylic component copolymerized therewith. This resin powder is used in industrial fields. However, it is not suited in cosmetic use for the following reason. It is synthesized by ring-opening polymerization of cyclic siloxane, which is equilibration reaction. Thus the emulsion after emulsion polymerization contains not only the polysiloxane, but also 5 to 10% by weight of residual cyclic siloxane. During storage or on use of the emulsion, the cyclic siloxane will volatilize off, adversely affecting physical stability and tactility. The amount of cyclic siloxane may be reduced by drying the emulsion into a powder, although the problem still remains unsolved. Therefore, it is desired to reduce the amount of residual cyclic siloxane in order that the emulsion may be used in the cosmetic application.
Under the circumstances, there is a desire to have a silicone-acrylic copolymer resin which is acceptable in the cosmetic application and has improved properties including extensibility, light feeling of quality, and soft tactility.
Citation List
Patent Document 1: JP-A H07-196815
Patent Document 2: JP-A 2001-151626
Patent Document 3: JP-A H03-162442
Patent Document 4: JP-A H04-342513
Patent Document 5: JP-A H05-078681